This invention relates to an improvement in planing machines for use in dimensioning rough sawn lumber which is moved normally through the mill at speeds of between 400 and 750 feet per minute. The planing machine of the present invention utilizes an endless abrasive belt driven about a contact drum positioned with its axis transverse to the direction of movement of the lumber at an angle of between about 5 and 15 degrees with respect to the direction of travel of the lumber.